Popular conventional lighting panels use either incandescent or fluorescent light sources. Conventional light fixtures are fragile, heavy in weight, difficult to manufacture, and have many replacement components such as ballasts, which are potential failures in addition to the fluorescent bulb.
In contrast, contemporary light sources, such as light emitting diodes, are substantially lighter in weight, more energy efficient and gradually age, rather than catastrophically fail. When the thermal and electronic drive characteristics are properly managed, light-emitting diode (LED) products are predicted to still deliver an average of 70% of initial intensity after 50,000 hours of operation, which at 12 hours per day, 365 days per year, amounts to a lifetime of 11 years. The direct nature of LEDs can result in efficiencies approaching 200 lumens per watt of electric power.
LEDs have many other desirable features. They are fully dimmable without color variation. They instantly turn on, have full color, and emit more light and less heat than other sources. LEDs can be sorted for photometric luminous, flux (in lumens), color, wavelength, and forward voltage. They are also extremely durable, and contain no harmful mercury vapors, such as those used in fluorescent light sources.
LED benefits are based on good thermal system design to achieve the best efficiency and reliability. The LED absolute maximum thermal ratings should be maintained for LED junction and printed circuit board temperature. The temperature of an LED should be managed in order to achieve the LED's maximum rated life. Thermal resistance causes a temperature difference between the source of the heat and the exit surface for heat. The less heat retained by the LED, the better its performance and the longer its lifetime. Despite the advantages of LEDs over other light sources, current designs have several problems.
Contemporary LED lighting panels are of two designs: One is waveguide-edge illumination with the light directed into a transparent or translucent waveguide and the LEDs placed along the perimeter of a panel. These panels are quite heavy (a 2′×2′ waveguide weighs 6-12 lbs.) and require the LEDs with the incumbent thermal loading on the perimeter. The need to use high power LEDs, due to the limited perimeter available, further exacerbates the thermal problem. The second is direct illumination with the light output from the LED die pointed towards a diffusive panel some distance away. In its simplest form, the LEDs deliver an intensity profile to the observer with many hot spots, which is unpleasant to look at. To eliminate this unpleasant look, diffuser panels are often used to soften the glare. The highest amount of softening is seen with the lowest value of transmission. These diffusers lower the efficiency of the panels' output due to this low transmission. In order to achieve a reasonably uniform illumination, complex optics and a substantial depth must be provided. This configuration—with the LEDs mounted on a top panel complicates the LEDs and the thermal management of the environment by concentrating the waste heat in the closed space between the fixture and the ceiling.